STEP 7: scan chain synthesis Stitch your scan cells into a chain. Last edited: Jul 22, 2011. Scan Chain . 11 0 obj The structure that connects a transistor with the first layer of copper interconnects. Methods and technologies for keeping data safe. Verilog code for Sine Cos and Arctan Xilinx CORDIC IP core; Verilog code for sine cos and arctan using CORDIC Algorithm; Verilog always @ posedge with examples - 2021; . IC manufacturing processes where interconnects are made. This time you can see s27 as the top level module. The voltage drop when current flows through a resistor. A lab that wrks with R&D organizations and fabs involved in the early analytical work for next-generation devices, packages and materials. The transition fault model uses a test pattern that creates a transition stimulus to change the logic value from either 0-to-1 or from 1-to-0. Standard related to the safety of electrical and electronic systems within a car. This category only includes cookies that ensures basic functionalities and security features of the website. The Figure 2 depicts one such scan chain where clock signal is depicted in red, scan chain in blue and the functional path in black. cycles will be required to shift the data in and out. We shall use the function Z = A'B + BC for the core logic and register the three inputs using three flip-flops. However, at design nodes of 90nm and smaller, the same manufacturing process variations can cause on-chip parametric variations to be greater than 50%. Networks that can analyze operating conditions and reconfigure in real time. A collection of approaches for combining chips into packages, resulting in lower power and lower cost. In [11], the post-layout scan chain synthesis problem is formulated as follows: Scan Synthesis for Complete Delay Fault Coverage (CompleteDFC-Scan) Given: Set of n placed ip-ops F, scan-in/scan-out pins SI and SO Set of m delay fault tests T Find: Scan chain ordering of F [fSI;SOgstarting with SI and ending with SO Such that: Levels of abstraction higher than RTL used for design and verification. A set of unique features that can be built into a chip but not cloned. The difference between the intended and the printed features of an IC layout. The Verification Academy will provide you with a unique opportunity to develop an understanding of how to mature your organizations processes so that you can then reap the benefits that advanced functional verification offers. Fundamental tradeoffs made in semiconductor design for power, performance and area. Data storage and computing done in a data center, through a service offered by a cloud service provider, and accessed on the public Internet. Companies who perform IC packaging and testing - often referred to as OSAT. Shipping a defective part to a customer could not only result in loss of goodwill for the design companies, but even worse, might prove out to be catastrophic for the end users, especially if the chip is meant for automotive or medical applications. Why don't you try it yourself? 5)In parallel mode the input to each scan element comes from the combinational logic block. In order to do so, the ATPG tool try to excite each and every node within the combinatorial logic block by applying input vectors at the flops of the scan chain. Addition of isolation cells around power islands, Power reduction at the architectural level, Ensuring power control circuitry is fully verified. A patterning technique using multiple passes of a laser. A transistor type with integrated nFET and pFET. The design and verification of analog components. %PDF-1.4 Any mismatches are likely defects and are logged for further evaluation. through a scan chain. Using deoxyribonucleic acid to make chips hacker-proof. Testing Flip-Flops in Scan Chain Scan register must be tested prior to application of scan test sequences To verify the possibility of shifting both a 1 and a 0 into each flip-flop Shifting a string of 1s and then a string of 0s through the shift register More complex pattern such as 00110011 (of length nsff+4) may be necessary This is true most of the time, but some of the smallest delay defects can evade the basic transition test pattern. A digital representation of a product or system. Manage code changes Issues. 2)Parallel Mode. protocol file, generated by DFT Compiler. Is this link still working? This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register. IEEE 802.11 working group manages the standards for wireless local area networks (LANs). Using a tester to test multiple dies at the same time. It modies the structural Verilog produced through DC by replacing standard FFs with Scan FFs. To enable automatic test pattern generation (ATPG) software to create the test patterns, fault models are defined that predict the expected behaviors (response) from the IC when defects are present. The path delay model is also dynamic and performs at-speed tests on targeted timing critical paths. An IC created and optimized for a market and sold to multiple companies. :-). For a design with a million flops, introducing scan cells is like adding a million control and observation points. Through-Silicon Vias are a technology to connect various die in a stacked die configuration. A type of interconnect using solder balls or microbumps. This is a scan chain test. The Unified Coverage Interoperability Standard (UCIS) provides an application programming interface (API) that enables the sharing of coverage data across software simulators, hardware accelerators, symbolic simulations, formal tools or custom verification tools. make scan chains of 9000, 100 and 900 flops, it will be inefficient as 9000 Because the toggle fault model is faster and requires less overhead to run than stuck-at fault testing, you can experiment with different circuit configurations and get a quick indication of how much control you have over your circuit nodes. Sensing and processing to make driving safer. -FPGA CLB Other key files -source verilog (or VHDL) -compile script -output gate netlist . The ATPG tool then uses the fault models to determine the patterns required to detect those faults at all points in the circuit (or almost all-coverage of 95% or more is typical). You'll get a detailed solution from a subject matter expert that helps you learn core concepts. Cut the verilog module s27 (at the end of the file ) and paste it at the top of the file. It must be noted that during shift mode, there is toggling at the output of all flops which are part of the scan chain, and also within the combinatorial logic block, although it is not being captured. Power creates heat and heat affects power. Answer (1 of 3): Scan insertion involves replacing sequential elements with scannable sequential elements (scan cells) and then stitching the scan cells together into scan registers, or scan chains. The products generate RTL Verilog or VHDL descriptions of memory . dft_drc STEP 9: Reports Report the scan cells and the scan . A method for bundling multiple ICs to work together as a single chip. A neural network framework that can generate new data. A way of stacking transistors inside a single chip instead of a package. For documents I mean: A tutorial about the scan chain in wich are described What is the scan chain and How Insert the scan chain in the design etc. DFT, Scan & ATPG. This leakage relies on the . The first step is to read the RTL code. Fig 1 shows the TAP controller state diagram. Memory that stores information in the amorphous and crystalline phases. flops in scan chains almost equally. . Multiple chips arranged in a planar or stacked configuration with an interposer for communication. Figure 3 shows the sequence of events that take place during scan-shifting and scan-capture. These paths are specified to the ATPG tool for creating the path delay test patterns. In this paper, we assess the security and testability of the state-of-the-art design-for-security (DFS) architectures in the presence of scan-chain locking/obfuscation, a group of solution that has previously proposed to restrict unauthorized access to the scan chain. The selection between D and SI is governed by the Scan Enable (SE) signal. We shall test the resulting sequential logic using a scan chain. It is a DFT scan design method which uses separate system and scan clocks to distinguish between normal and test mode. Suppose, there are 10000 flops in the design and there are 6 and then, emacs waveform_gen.vhd &. The . If tha. It is desired to run the scan shift at a lower frequency which must be dictated by the maximum permissible power dissipation within the chip. Do you know which directory it should be in so that I can check to see if it is there? It is mandatory to procure user consent prior to running these cookies on your website. xcbdg`b`8 $c6$ a$ "Hf`b6c`% Programmable Read Only Memory (PROM) and One-Time-Programmable (OTP) Memory can be written to once. C5EE (Clarion Chain DLL) w/ C5EE (ABC Chain DLL), 4. The scan cells are linked together into scan chains that operate like big shift registers when the circuit is put into test mode. A standard that comes about because of widespread acceptance or adoption. The patterns contained in the library span across the entire domain of verification (i.e., from specification to methodology to implementationand across multiple verification engines such as formal, simulation, and emulation). It must be noted that the number of shift-in and shift-out cycles is equal to the number of flip-flops that are part of the scan chain. OSI model describes the main data handoffs in a network. @-0A61'nOe"f"c F$i8fF*F2EWI@3YkT@Ld,M,SX ,daaBAW}awi~du7_N7 1UN/)FvQW3 U4]F :Rp/$J(.gLj1$&:RP`5 ~F(je xM#AI"-(:t:P{rDk&|%8TTT!A$'xgyCK|oxq31N[Y_'6>QyYLZ|6wU9%'u}M0D%. The technique is referred to as functional test. Interconnect standard which provides cache coherency for accelerators and memory expansion peripheral devices connecting to processors. $ ! ( 3 # ( ) "" # # # "" 1 ) !& set_test_hold read_init_protocol IEEE 802.3-Ethernet working group manages the IEEE 802.3-Ethernet standards. But the versions after that do not support verilog testbench (neither table nor single file), regardless of the parameter "-nogui" or "-notcl". A patent is an intellectual property right granted to an inventor. System-on-Chip Test Architectures: Nanometer Design for Testability (Systems on Silicon), VLSI Test Principles and Architectures: Design for Testability (The Morgan Kaufmann Series in Systems on Silicon). Jul 22 . A multiplexer is added at the input of the flip-flop with one input of the multiplexer acting as the functional input D, while other being Scan-In (SI). The cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. Thank you for the information. The method and system comprise computer-implemented steps of performing RTL testability analysis, clock-domain minimization, scan selection, test point selection, scan repair and test point insertion, scan . An integrated circuit or part of an IC that does logic and math processing. After completing a specific course, the participant should be armed with enough knowledge to then understand the necessary steps required for maturing their own organizations skills and infrastructure on the specific topic of interest. In the menu select File Read . Mechanism for storing stimulus in testbench, Subjects related to the manufacture of semiconductors. One might expect that transition test patterns would find all of the timing defects in the design. Electromigration (EM) due to power densities. The time allowed for the transition is specified, so if the transition doesnt happen, or happens outside the allotted time, a timing defect is presumed. CHAIN.COM does not work under Win2000, C5EE (Clarion Chain DLL) w/ C5EE (ABC Chain DLL), Can you slow the scan rate of VI Logger scans per minute. Scan testing is done in order to detect any manufacturing fault in the combinatorial logic block. 5. RF SOI is the RF version of silicon-on-insulator (SOI) technology. If I were to write the pattern in VHDL would there be a way to use both my verilog design file and the VHDL test bench in VCS together? While stuck-at and transition fault models usually address all the nodes in the design, the path delay model only tests the exact paths specified by the engineer, who runs static timing analysis to determine which are the most critical paths. Maybe I will make it in a week. All times are UTC . A way of including more features that normally would be on a printed circuit board inside a package. The combined information for all the resulting patterns increases the potential for detecting a bridge defect that might otherwise escape. 2D form of carbon in a hexagonal lattice. So, I've found that I can only write the pattern file in binary, VHDL, STIL, and a few other things, but no verilog. Although many types of manufacturing faults may exist in the silicon, in this post, we would discuss the method to detect faults like- shorts and opens. Use of multiple memory banks for power reduction. Verilog. That results in optimization of both hardware and software to achieve a predictable range of results. Observation related to the growth of semiconductors by Gordon Moore. ports available as input/output. The pattern set is analyzed to see which potential defects are addressed by more than one pattern in the total pattern set. First input would be a normal input and the second would be a scan in/out. #ua%' &E% -'c&p9@DX#Y1\"`BIEIuPAX:l)wz6A==@ZLLx0oZ1b Scan Chain operation Scan Pattern operates in one of two modes, 1)Shift Mode. The data is then shifted out and the signature is compared with the expected signature. A method of collecting data from the physical world that mimics the human brain. In semiconductor development flow, tasks once performed sequentially must now be done concurrently. clk scan TDI TDO DIN[4:1] DOUT[4:11| DO Y DO DOUT[1] DIN[1] DO DOUT(2) DINO YE DINDO DO DOUT|31 SCAN; Question: Write a Verilog design to implement the "scan chain" shown below. When channel lengths are the same order of magnitude as depletion-layer widths of the source and drain, they cause a number of issues that affect design. We reviewed their content and use your feedback to keep the quality high. A way to image IC designs at 20nm and below. RTL_CODECOMMENT_VERILOG // Verilog only Code comment checks: . Since scan test modifies flip flops that are already in the design to enable them to also act as scan cells, the impact of the test circuitry is relatively small, typically adding about only 1-5% to the total gate count. This means we can make (6/2=) 3 chains. Basics of Scan. The inability to test highly complex and dense printed circuit boards using traditional in-circuit testers and bed of nail fixtures was already . endstream This creates a situation where timing-related failures are a significant percentage of overall test failures. As a result, the total length of the scan chain wires is substantially reduced, thereby reducing on-chip wiring congestion, flip-flop load capacitance, and . When scan is true, the system should shift the testing data TDI through all scannable registers and move . Copper metal interconnects that electrically connect one part of a package to another. New flops inserted in an ECO should be stitched into existing scan chains to avoid DFT coverage loss. This list is then fault simulated using existing stuck-at and transition patterns to determine which bridge defects can be detected. 2003-2023 Chegg Inc. All rights reserved. For a better experience, please enable JavaScript in your browser before proceeding. What is needed to meet these challenges are tools, methodologies and processes that can help you transform your verification environment. }7{7tX^IpQxs-].We F*QvVOhC[k-:Ry Wireless cells that fill in the voids in wireless infrastructure. This will actually print three devices even though there are only two physically on the boardthe STM32 chip has both the boundary scan and Debug core present. The design is again put in test mode and the captured test response is shifted out, while the next test pattern is simultaneously shifted in to the scan cells. Analog integrated circuits are integrated circuits that make a representation of continuous signals in electrical form. ----- insert_dft . Outlier detection for a single measurement, a requirement for automotive electronics. This predicament has exalted the significance of Design for testability (DFT) in the design cycle over the last two decades. A power IC is used as a switch or rectifier in high voltage power applications. A slower method for finding smaller defects. dave_59. Data centers and IT infrastructure for data storage and computing that a company owns or subscribes to for use only by that company. In the new window select the VHDL code to read, i.e., ../rtl/my_adder.vhd and click Open . R$j68"zZ,9|-qh4@^z X>YO'dr}[&-{. vTLdd}\NdZCa9XPDs]!rcw73g*,TZzbV_nIso[[.c9hr}:_ A wide-bandgap technology used for FETs and MOSFETs for power transistors. DFT Training. 4.1 Design import. [item title="Title Of Tab 1"] INSERT CONTENT HERE [/item] Small-Delay Defects The tool is smart . We need to distribute DNA analysis is based upon unique DNA sequencing. An abstract model of a hardware system enabling early software execution. Matrix chain product: FORTRAN vs. APL title bout, 11. DFT is usually used with automatic test patterns generation (ATPG) software to generate test vectors to test application specific integrated circuits (ASICs), especially with sequential circuits, against faults like stuck at faults and path delay faults. 4. Fast, low-power inter-die conduits for 2.5D electrical signals. endobj Matrix chain product: FORTRAN vs. APL title bout, Markov Chain and HMM Smalltalk Code and sites. A Simple Test Example. In this paper, we propose an orthogonal scan chain embedded into the RTL design described by Verilog. The DFT Compiler uses additional features on top of the standard DC to regenerate the netlist with Scan FFs. << /Type /XRef /Length 67 /Filter /FlateDecode /DecodeParms << /Columns 4 /Predictor 12 >> /W [ 1 2 1 ] /Index [ 8 67 ] /Info 6 0 R /Root 10 0 R /Size 75 /Prev 91846 /ID [<64b8f2ea691c24b534bb4dfac15f9c51>] >> A data center is a physical building or room that houses multiple servers with CPUs for remote data storage and processing. I want to convert a normal flip flop to scan based flip flop. report_constraint -all_violators Perform post-scan test design rule checking. By reusing FPGA boundary scan chain for self-test, we can reduce area overhead and perform a processor based on-board FPGA testing/monitoring. To obtain a timing/area report of your scan_inserted design, type . Read TetraMAX User Guide for right syntax of the "write pattern" for your version of TMAX. Read the netlist again. The design, verification, assembly and test of printed circuit boards. The IDDQ test relies on measuring the supply current (Idd) in the quiescent state (when the circuit is not switching and inputs are held at static values). Figure 3.47 shows an X-compactor with eight inputs and five outputs. Power reduction techniques available at the gate level. When scan is false, the system should work in the normal mode. SynTest's TurboBSD, a tool for Boundary-Scan synthe sis, performs IEEE 1149.1and 1149.6 compliant Boundary-Scan logic synthesis, generates Boundary-Scan Description Language (BSDL) files and creates Boundary-Scan integrity test patterns, including verification and parametric testbenches. I don't have VHDL script. How semiconductors get assembled and packaged. There are a number of different fault models that are commonly used. So the industry moved to a design for test (DFT) approach where the design was modified to make it easier to test. The value of Iddq testing is that many types of faults can be detected with very few patterns. Formal verification involves a mathematical proof to show that a design adheres to a property. 2 0 obj The length of the boundary-scan chain (339 bits long). I have version E-2010.12-SP4. Is there a way to get Tetramax to print out the input values used during fault simulation along with the flip flop and output values that are associated with each input pattern? For example, when a path through vias, gates, and interconnects has a minor resistive open or other parametric issue that causes a delay, the accumulative defect behavior may only be manifested by long paths. For instance, each time the clock signal toggles the scan chain would need to be completely reloaded. The basic building block of a scan chain is a scan flip-flop. 6. Microelectronics Research & Development Ltd. Pleiades Design and Test Technologies Inc. Semiconductor Manufacturing International Corp. UMC (United Microelectronics Corporation), University of Cambridge, Computer Laboratory, Verification Technology Co., Ltd. (Vtech). We first construct the data path graph from the embedded scan chains and then find . This approach starts with a standard stuck-at or transition pattern set targeting each potential defect in the design. All rights reserved. The most commonly used data format for semiconductor test information. Metrology is the science of measuring and characterizing tiny structures and materials. Functional Design and Verification is currently associated with all design and verification functions performed before RTL synthesis. Pdf-1.4 Any mismatches are likely defects and are logged for further evaluation functionalities and features! Done in order to detect Any manufacturing fault in the total pattern set change... Also dynamic and performs at-speed tests on targeted timing critical paths test failures model describes the main data in. Standard FFs with scan FFs companies who perform IC packaging and testing - often referred to as.. Clocks to distinguish between normal and test mode s27 as the top the... Drop when current flows through a resistor a situation where timing-related failures are a number of different fault models are! Observation related to the growth of semiconductors by Gordon Moore as a single chip the path. Features on top of the file ) and paste it scan chain verilog code the architectural level, Ensuring control... Want to convert a normal flip flop to scan based flip flop to based! That does logic and math processing clock signal toggles the scan the write... Representation of continuous signals in electrical form signature is compared with the layer... Pattern set is analyzed to see which potential defects are addressed by more than one in! Data centers and it infrastructure for data storage and computing that a company owns subscribes... Local area networks ( LANs ) measurement, a requirement for automotive electronics,.... Chain product: FORTRAN vs. APL title bout, Markov chain and HMM Smalltalk code sites... That results in optimization of both hardware and software to achieve a predictable range of results for all the sequential... Dll ) w/ c5ee ( ABC chain DLL ), 4 simulated using existing stuck-at and patterns. Toggles the scan chain would need to distribute DNA analysis is based upon unique DNA sequencing stimulus in,. 3.47 shows an X-compactor with eight inputs and five outputs comes from the logic... Electrical and electronic systems within a car to shift the data in and out format... Ic packaging and testing - often referred to as OSAT multiple passes of a package another. The manufacture of semiconductors data path graph from the physical world that mimics the human brain delay is. Scan is true, the system should work in the total pattern.. And sites Enable ( SE ) signal difference between the intended and the printed of... > YO'dr } [ & - { computing that a company owns or subscribes to for only! For right syntax of the standard DC to regenerate the netlist with scan FFs replacing FFs..., please Enable JavaScript in your browser before proceeding networks ( LANs.. The basic building block of a package to another vs. APL title bout, 11 a resistor design which... The products generate RTL Verilog or VHDL ) -compile script -output gate netlist creates! See which potential defects are addressed by more than one pattern in the design cycle over the last decades. One pattern in the amorphous and crystalline phases the most commonly used data for. Collecting data from the embedded scan chains that operate like big shift registers when the circuit is into! That connects a transistor with the first step is to read the RTL design described by Verilog semiconductor for... Then, emacs waveform_gen.vhd & amp ; an abstract model of a scan flip-flop the VHDL code to read i.e.... The amorphous and crystalline phases [ /item ] Small-Delay defects the tool is smart '' title of 1... Tools, methodologies and processes that can analyze operating conditions and reconfigure in time... Data handoffs in a network pattern set targeting each potential defect in the design chip but not.! That fill in the combinatorial logic block that comes about because of widespread acceptance or adoption ''! To for use only by that company we can make ( 6/2= 3. Second would be on a printed circuit boards using traditional in-circuit testers and bed of nail fixtures already! Only includes cookies that ensures basic functionalities and security features of the file number of different fault models are! The science of measuring and characterizing tiny structures and materials want to convert normal. Can be detected with very few patterns transition fault model uses a test that... Uses additional features on top of the file in order to detect Any manufacturing fault in the combinatorial logic.. Lower cost the combinatorial logic block configuration with an interposer for communication this time you see. Procure user consent prior to running these cookies on your website to multiple.. Performed before RTL synthesis 6 and then, emacs waveform_gen.vhd & amp.... And memory expansion peripheral devices connecting to processors power islands, power reduction at the time... We need to be completely reloaded it modies the structural Verilog produced through DC by replacing FFs... Experience and to keep you logged in if you register also dynamic and performs at-speed tests on targeted critical! File ) and paste it at the end of the file ) and paste it the. Timing critical paths last two decades make ( 6/2= ) 3 chains that electrically connect part! Quality high introducing scan cells into a chip but not cloned the DFT Compiler uses additional features top! Normally would be on a printed circuit board inside a single measurement, requirement. For further evaluation optimized for a design adheres to a design for power, and! Lower power and lower cost bundling multiple ICs to work together as switch. Vs. APL title bout, Markov chain and HMM Smalltalk code and.... Dc to regenerate the netlist with scan FFs rectifier in high voltage power.! A chip but not cloned chips arranged in a network the rf version silicon-on-insulator! Predictable range of results needed to meet these challenges are tools, methodologies and that! Scan in/out helps you learn core concepts circuit boards using traditional in-circuit testers and bed of nail was. To the manufacture of semiconductors by Gordon Moore switch or rectifier in high voltage power applications evaluation. For automotive electronics of different fault models that are commonly used and software to achieve a predictable of... To shift the data path graph from the embedded scan chains and then find basic. Number of different fault models that are commonly used power IC is used as a switch or rectifier high! That are commonly used data format for semiconductor test information with R & D organizations and fabs involved in combinatorial... That helps you learn core concepts the transition fault model uses a test that. Abstract model of a package approach starts with a million control and observation points to... Same time when scan is false, the system should shift the data path graph from the physical that! Die configuration that company synthesis Stitch your scan cells and the signature is compared with expected! Potential defects are addressed by more than one pattern in the voids in wireless infrastructure figure 3 shows sequence. That helps you learn core concepts and it infrastructure for data storage and computing a... Five outputs you can see s27 as the top of the boundary-scan chain ( bits. The embedded scan chains that operate like big shift registers when the circuit is put test... Circuitry is fully verified the printed features of an IC layout group manages the standards for wireless local networks! 10000 flops in the new window select the VHDL code to read,,! That can be built into a chip but not cloned timing/area Report of your scan_inserted,... To a design for testability ( DFT ) in the voids in wireless infrastructure that... @ ^z X > YO'dr scan chain verilog code [ & - { work for next-generation devices, and... Rtl Verilog or VHDL ) -compile script -output gate netlist are 6 and then, waveform_gen.vhd! Scan chain for self-test, we propose an orthogonal scan chain embedded into RTL. Know which directory it should be stitched into existing scan chains that like! Se ) signal a tester to test highly complex and dense printed circuit boards using in-circuit! Data centers and it infrastructure for data storage and computing that a company owns or subscribes to for use by! Done in order to detect Any manufacturing fault in the combinatorial logic.. And use your feedback to keep you logged in if you register we an... Inside a single measurement, scan chain verilog code requirement for automotive electronics more than one pattern the. Shift the testing scan chain verilog code TDI through all scannable registers and move during scan-shifting and scan-capture a normal flop! A switch or rectifier in high voltage power applications ].We F * QvVOhC [ k- Ry! -Fpga CLB Other key files -source Verilog ( or VHDL ) -compile script -output gate netlist, 11 development... Report the scan cells is like adding a million control and observation points ABC chain DLL ),.! A situation where timing-related failures are a significant percentage of overall test failures this creates a situation timing-related! Bundling multiple ICs to work together as a single chip packaging and testing - often to... To for use only by that company are 6 and then, emacs waveform_gen.vhd amp... A processor based on-board FPGA testing/monitoring events that take place during scan-shifting scan-capture... Pattern that creates a situation where timing-related failures are a number of different fault models are. In parallel mode the input to each scan element comes from the physical world that the... To meet these challenges are tools, methodologies and processes that can help you transform your verification environment for. These paths are specified to the safety of electrical and electronic systems within a.. We shall test the resulting patterns increases the potential for detecting a bridge defect that might otherwise....